Process of conditioning wood for impregnation with preservatives



Dec. 29, w, P ARNOLD 1,838,291

PROCESS OF CONDITIONING WOOD FOR IMPREGNATION WITH PRESERVATIVES Filed July 11, 1929 checking,

Patented Dec. 29, 1931 UNITED STATES PATENT OFFICE,

WALTER PAUL ARNOLD, 0F ORRVILLE, OHIO, ASSIGNOB, BY MESNE ASSIGNMENTS, TO THE WOOD PRESERVING'CORIPORATION, OF PITTSBURGH, EENNSYLVANIA, A COR- PORA'IION OF DELAWARE PROCESS OF CONDITIONING WOOD FOR Application filed July 11,

This invention relates to wood conditioning, and especially to a process of prepar ng wood for impregnation with a preservative.

An object of the invention is to royide a process of conditioning wood'which is sample, may be easily, performed at low cost, is relatively rapid, and which effects substantialremoval of moisture from the wood and mimmizes the checking which characterizes some prior processes.

A particular object of the inventlon is to provide a process of the type referred to which is especially adapted to the preparation of wood for impregnation with preservative materials, and which may be practiced in connection with the apparatus used for wood impregnation without requlrlng material change of such apparatus.

For purposes of illustration, the invention may be described in connection with its application to wood impregnation processes, and the accompanying drawing schematically represents an apparatus adapted to such use.

This invention comprises an improvement upon the steaming process heretofore used in conditioning wood and in which the wood is first steamed under pressure and then subjected to vacuum. This prior steaming process does not remove as much moisture as is desirable, and causes considerablechecking,

which factors prevent proper impregnation or cause the impregnated product to be of inferior quality.

The invention is predicated upon my discover that a much greater moisture removal may e effected, and with substantially less if in addition to impregnation with steam the wood is also impre mated with an aeriform fluid prior to SuTJjecting it to vacuum. The treatment preferably comprises successive pressure impregnation with an aeriform fluid and then with steam, and the moisture is then withdrawn from the wood by means of high vacuum, the combination of aeriform fluid and steam in the pores and cells resulting in substantially greater moistureremoval than heretofore,-

and materially reducing checking of the wood. v

IMPREGNATION WITH ransnnvn'rrvns 1929. Serial 110.37%404.

In the preferred practice of the invention the wood in a closed chamber is subjected to aeriform fluid under high pressure to cause deep penetration of the fluid into the wood and its cells, and the aeriform fluid in the chamber is then replaced with steam at a lower pressure. Most suitably, air is used as the aeriform fluid, and the steam pressure is preferably maintained below about 30 pounds per square inch. After the wood has been steamed, the steam pressure is relieved, and a high vacuum is rapidly created in the chamber, whereupon a large proportion of the moisture, such as sap, condensed steam and other liquid, in the wood is withdrawn.

As thus treated, the wood is in condition for proper and highly satisfactory im pregnation with a preservative material, which may be accomplished in any desired manner, for example by any of the empty cell methods now practiced.

The process according to the invention may advantageously be carried out in connection with the high pressure system of wood preserving, for example in the apparatus shown in the drawing. This apparatus comprises a horizontal treating chamber 1 adapted to withstand high pressure, and provided at one end with a pressure-tight closure door 2. The chamber is connected by piping 3 to a compressed air tank 4 in which air is compressed under high pressure, for example 350 pounds per square inch, by a compressor 5. Steam is supplied to the chamber from a boiler 6 through piping 7, and the chamber is evacuated by a vacuum pump 8 connected thereto by piping 9, a condenser 10 being inserted in the line. The chamber is also provided with a vent pipe 11 provided with a shut ofl valve 12, and valves are provided in the air, steam and vacuum lines.

Green or partially seasoned wood is placed in chamber 1, door 2 is closed, and the wood subjected to high pressure air from tank 4:. The degree of penetration of the air into the wood depends upon the pressure and the length of exposure. In general, it is preferred to subject the wood to an air pressure of about 100 pounds per square inch, and an exposure to this pressure of from one-half to a vacuum as practicable one and one-half hours is usually suflicient to cause deep penetration. The air pressure is now cut ofl, and the air in the chamber is replaced by steam. It is preferred to relieve the pressure in chamber 1 through vent pipe 11 before opening valve 13 in steam line 7. The boiler is operated at high enough pressure to quickly raise the steam pressure inthe chamber to the maximum treating pressure, which should not in general exceed about 30 pounds per square inch. In order to avoid injury to the wood, the duration of steaming at the maximum pressure should not exceed about 2 hours for most of the woods which are impregnated with a reservative. When steaming is complete, t e steam is shut off and vent pipe 11 is opened to relieve the pres sure. Valve 12 is then closed, and the chamber is rapidly evacuated by means of pump 8 for withdrawing moisture from the wood. To satisfactorily remove the moisture, as high with such apparatus should be produced, and the vacuum maintained until the rate of condensation of liquid in condenser 7, or by an equivalent means, shows that the moisture-removing step is complete, or substantially so.

This successive impregnation of the green or partially seasoned wood with an aeriform fluid and then with steam, prior to vacuumizing, causes a much greater moisture removal than in prior steaming processes. Ap-

parently this is due to the fact that liquid cannot readily penetrate the wood cells which normally contain plant liquid, whereas air or similar fluid under high pressure is capable of more ready penetration into the cells, renders them more susceptible to steaming, and in general renders possible much greater moisture removal and minimizes checking. In consequence of the better moisture removal, the wood may be impregnated with preservative more readily, and, because checking is reduced, the integrity and strength of the wood is maintained.

The wood may be, and preferably is, impregnated in the conditioning chamber. This may be accomplished by any process desired, but because of the empty-cell condition of the wood, and because high air pressure is available in the preferred form of apparatus, the high pressure impregnation methods may conveniently be used. After the vacuumizing step, preservative liquid, such as hot creosote from a Rueping tank 14, or

, zinc chloride or other preservative, is run into chamber 1 through piping 15, and pressure is applied through a measuring tank-16 connected to air tank 4 by a branch line 17 and to the chamber by piping 18, the pressure being maintained until the desired preservative impregnation has been attained.

According to the provisions of the patent statutes, I have explained the principle and mode of operation of my invention and have described what I now consider to be the best way of practicing it. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1; A process of conditioning wood for impregnation with a preservative, comprising SIlbJGCtiIlg the wood in a closed chamber to an aeriform fluid under pressure and for a time to cause deep penetration of said fluid into the wood, replacing said fluid by steam under pressure, and then creating a high vacuum in the chamber to withdraw moisture from the wood.

2. A process of conditioning wood for impregnation with a preservative, comprising subjecting the wood in a closed chamber to air under a pressure adapted to cause deep penetration of air into the wood, replacing the air in the chamber by steam at a lower pressure, and subsequently creating a high vacuum in the chamber to withdraw moisture from the wood.

3. A process of conditioning wood for impregnation with a preservative, comprising subjecting the wood in a closed chamber to air under a high pressure and for a period of time sufficient to cause deep penetration of air into the wood, replacing the'air in the chamber with steam at less than pounds per square inch pressure, releasing the steam pressure, and rapidly applying a high vacuum to withdraw moisture from the wood.

4. In a wood conditioning process, the steps comprising successively impregnating the wood with an aeriform fluid and then with steam, and subsequently subjecting the wood to high vacuum to withdraw moisture from the wood.

5. In a wood conditioning process the steps comprising pressure-impregnating the wood successively with air under high pressure and then with steam under a pressure less than about 30 pounds per square inch, and subsequently subjecting the wood to a high vacuum to cause extraction of moisture from the cells .of the wood.

In testimony whereof, I sign my name.

WALTER PAUL ARNOLD.

about 30 i 

